The objective of this research is to examine the contribution of the amygdala central nucleus to learning and memory processes. To this end we are using the rabbit as an experimental animal, the defensively conditioned heart rate and nictitating membrane responses as behavioral measures, and a combination of neurochemical, neuroanatomical and lesion techniques. Using an aversive Pavlovian conditioning paradigm, rabbits receiving either small or large lesions primarily confined to the central nucleus demonstrate a significant attenuation of the conditioned cardiodecelerative heart rate response to the conditioned stimulus. In addition, rabbits receiving pre-conditioning bilateral microinjections of the beta-adrenergic antagonist, d1-propranolol, into the dorsal amygdala at the level of the central nucleus, an area of high adrenergic terminal concentration, demonstrate a significant attenuation of the conditioned bradycardia response when compared to vehicle-injected and unoperated control groups. Rabbits receiving the same dose of d-propranolol did not exhibit a comparable conditioning deficit. Combined administration of d1-propranolol and 1-isoproterenol, a beta-adrenergic agonist, reduced the conditioning impairment produced by d1-propranolol. Finally, using the horseradish peroxidase technique, we have demonstrated a direct projection from the central nucleus to the nucleus solitarius-vagal dorsal motor nucleus complex, a site of origin of vagal cardio-inhibitory fibers which may mediate the conditioned decelerative response in the rabbit. In summary, the combined results suggest the possibility that the central nucleus may exert a rather direct influence on the cardiovascular system and that this nucleus may influence cardiovascular responding during aversive conditioning.